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Impact of Late Cretaceous-Early Palaeogene Tectonics on Hydrocarbon-Bearing Basins of Mainland Southeast Asia

Morley, Christopher K.
PTTEP, Bangkok, Thailand.

The Late Cretaceous-early Palaeogene in Mainland Southeast Asia is a time period that is poorly represented by outcropping sediments, or known basins (one exception being western Myanmar). Granitic plutonic activity of this age in Thailand and Myanmar point to significant tectonic activity during this time, which appears to be subduction-related. The tradition view of SE Asian tectonics has emphasized the onset of extension during the Eocene or Oligocene, and the development of major strike-slip faults (e.g. Ailao Shan-Red River, Mae Ping, Three Pagodas, Ranong, Khlong Marui fault zones) during the Oligocene as a consequence of India-Eurasian collision. It has been suggested that many of the rift basins are related to strike-slip faults. However, there is a growing body of evidence to indicate that Late Cretaceous-early Palaeogene deformation was highly significant, and had a strong impact on the subsequent development of basins in the Gulf of Thailand and onshore. Some of the major strike-slip faults did not just reactivate old Indosinian orogeny faults, or begin activity during the Oligocene, but instead were active during the Late Cretaceous-Eocene. In the hydrocarbon province of NE Thailand important folding, uplift and erosion of the Khorat Group occurred during the Palaeogene. This deformation continued offshore into the Gulf of Thailand and Peninsular Thailand. The impact of this deformation on conditioning the crust for the subsequent development of extensional basins remains to be fully evaluated. One possibility is that rift basins development is at least partially related to extensional collapse of crust thickened during earlier transpressional deformation. The widespread occurrence of low-angle normal faults, and occasional example of small, Palaeogene metamorphic core complexes point to unusual crustal conditions during rift basin development. Structural and radiometric age dating studies of onshore outcrops, and future drilling in the Gulf of Thailand to pre-Cenozoic objectives, and exploration in the Tonle Sap Basin is likely to result in significant advances to our understanding of the pre-rift controls on structural characteristics of the hydrocarbon-bearing Cenozoic syn-rift and post-rift basins particularly in the Gulf of Thailand.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012